The present invention relates to a method of improving germination by subjecting seeds to presowing hydration treatment. More particularly, it relates to a hydration treatment technology seeds prior to sowing for the purpose of achieving rapid and uniform germination of seeds after sowing and improving the germinating rate even in an adverse environment.
Once sowed, seeds germinate after a certain period of time if environmental conditions such as moisture, temperature, oxygen and light are all appropriate.
During this pregermination period from sowing to germination, various metabolic processes proceed within seeds. The length of said period varies depending on the degree of maturity of each individual seed, the kind of seed, and such environmental factors such as temperature and moisture content. Shortening of said pregermination and attaining rapid and uniform germination will facilitate cultivation management and, in commercial production, offers such advantages as reduction in production costs and labor.
For such purposes, seeds are subjected to hydration treatment prior to sowing. Thus, a method so far practiced in spinach cultivation, for instance, comprises immersing seeds in well water for a day (germination enhancing treatment), followed by sowing. In recent years, other seed hydration techniques, such as priming, osmoconditioning and matriconditioning, have been developed and proved to be effective in enhancing germination and/or in improving the germination rate in adverse environments, among others.
The principle of the seed hydration technology such as priming, germination following sowing by supplying seeds before sowing with water and treating them for a time and at a temperature sufficient to cause the seeds to imbibe sufficient water to enhance resultant plant vigor but insufficient to cause seeds sprouting. Among the various seed hydration techniques reported to date as the fruits of research and development work, the following four may be mentioned as principal ones:
(1) Priming
This technique was developed by W. Heydecker et al. in 1974 and comprises osmotically controlling the water supply to seeds using, as a medium, an aqueous solution of a water-soluble polymer (polyethylene glycol, sodium polypropenate, etc.) or an aqueous salt solution (W. Heydecker, J. Higgins and R. L. Gulliver, 1973, Nature (London) 246s42-44; W. Heydecker, 1974, Univ. Nottingham Sch. Agr. Rep. 1973/1974:50-67; Zuo Weineng et al., 1987, Chinese Science Bulletin 32:1438).
(2) Drum priming
This technique developed by H. R. Rowse in 1987 comprises supplying seeds with water by spraying in a rotating drum to thereby directly control the weight of water to be supplied to seeds, without using any medium (British Patent 2192781).
(3) Solid matrix priming
This technique developed by A. G. Taylor et al. in 1988 comprises controlling the water supply to seeds using, as a medium, a pulverized leonardite shale material (Agro-Lig) (A. G. Taylor, D. S. Klein and T. H. Whitlow, 1988, Scientia Horticulturae 37 (1988) 1-11; U.S. Pat. No. 4,912,874; European Patent 0309551B1;W088/07318).
(4) Matriconditioning
This technique developed by A. A. Khan et al. in 1990 comprises controlling the water supply to seeds using, an a medium, a water-insoluble porous material (Micro-Cel E, Zonolite) (A. A. Khan, H. Miura, J. Prusinski and S. Ilyas, Proceedings of the Symposium on Stand Establishment of Horticultural Crops/Minneapolis, Minn., Apr. 4-6, 1990).
Common features of the four techniques mentioned above are that they are all seed hydration techniques to be performed on seeds prior to sowing and that only those various metabolic processes that proceed within seeds during the pregermination are artificially driven to completion prior to sowing by controlling the supply of water to seeds.
Differences among them are found in the respective water content controlling principles. In (1), a liquid is used as a medium and the water supply to seeds is controlled by the osmotic potential of the liquid. In (2), no medium is used and the water content is directly controlled in terms of weight of water. In (3) and (4), a water-insoluble solid medium is used and the water content is controlled by means of an osmoticum and/or a matric potential.
These techniques are comparably effective in improving germination but each has its drawbacks, as mentioned below.
The priming technique mentioned under (1) is not suited for large quantity treatment on a commercial scale since the polyethylene glycol solution or the like solution to be used has a high viscosity, the solubility of oxygen in the solution is low and time is required in drying seeds after treatment.
The drum priming technique mentioned under (2) is simple and clear-cut but is difficult to put into practice since precise mechanical control is required for regulating the quantity of water and accordingly the mechanical equipment and procedure become substantially complicated.
The techniques mentioned under (3) and (4), which make use of the matric potential or the like of a water-insoluble solid medium, can treat seeds in simple equipment and have solved the problem of oxygen supply. However, the powdery solid medium remains, adhering to the treated seeds, and it is difficult to separate it by sieving. The solid medium particles adhering to the seeds after treatment cause dust in the process of packaging and/or distribution of the seeds. This may also leads to serious impairment of the value of the seeds as commercial products.